Method of making porous inorganic bodies using water-soluble zirconium compounds

ABSTRACT

Disclosed are methods of making porous bodies of SiO2, Al2O3, and TiO2 having average pore diameters which closely approximate the particle size of the starting material used to form the porous bodies, thereby permitting the production of porous bodies having a very uniform pore size distribution such that the diameters of about 90 percent of the pores are within + OR - 20 percent of the average pore size of the material. The process involves forming a uniform slurry of metal oxide particles of SiO2, Al2O3, or TiO2 having substantially uniform particle size and a liquid binder consisting of a solution containing a water soluble zirconium compound, gently drying the slurry, and firing the mixture at a temperature below that at which the material sinters.

United States Patent [191 Messing [4 1 Oct. 7, 1975 METHOD OF MAKING POROUS INORGANIC BODIES USING WATER-SOLUBLE ZIRCONIUM COMPOUNDS [75] Inventor: Ralph A. Messing, Horseheads, NY. [73] Assignee: Corning Glass Works, Corning,

[22] Filed: Sept. 17, 1973 [2l] Appl. No.: 397,615

[52] U.S. Cl 252/455 R; 252/454; 252/461;

252/463, l06/86 [5 l] Int. Cl. B01] 29/06; B011 29/00; C04B 7/00 [58] Field of Search 252/454, 455 R, 461, 463;

Gordon [06/40 R X Heckelsbcrg 252/461 X [57] ABSTRACT Disclosed are methods of making porous bodies of SiO,, Al,O and TiO, having average pore diameters which closely approximate the particle size of the starting material used to form the porous bodies, thereby permitting the production of porous bodies having a very uniform pore size distribution such that the diameters of about 90 percent of the pores are within :20 percent of the average pore size of the material. The process involves forming a uniform slurry of metal oxide particles of Slog, AI,O or TiO, having substantially uniform particle size and a liquid binder consisting of a solution containing a water soluble zirconium compound, gently drying the slurry, and firing the mixture at a temperature below that at which the material sinters.

3 Claims, No Drawings METHOD OF MAKING POROUS INORGANIC BODIES USING WATER-SOLUBLE ZIRCONIUM COMPOUNDS RELATED APPLICATIONS U.S. Pat. application Ser. No. 332,807 filed on Feb. l6, I973, entitled Enzymes Immobilized on Porous Inorganic Support Materials, now U.S. Pat. No. 3,850,75 l, and U.S. Pat. application Ser. No. 344,964, filed Mar. 26, I973 and entitled Method of Making Porous Inorganic Bodies," both applications filed in the name of R. A. Messing and assigned to the present assignee.

BACKGROUND OF THE INVENTION This invention relates generally to the production of porous bodies consisting of metal oxides. Specifically, the invention is concerned with the production of porous bodies of silica (SiO alumina (AI O or titania (TiO having a very closely controlled average pore diameter within the range of 100 A to I000 A. The porous bodies are especially suitable for the immobilization of proteins such as enzymes.

The importance of being able to make porous inorganic support materials having an average pore diameter between about 100 A and 1000 A is pointed out in my copending application Ser. No. 332,807. In that application, it is shown that the immobilization of enzymes on porous, essentially water-insoluble, inorganic support materials can be greatly optimized by using porous inorganic support materials having a closely controlled average pore diameter which is related to the size of the enzyme molecule and/or the molecular size of the substrate upon which the enzyme acts. Accordingly, by knowing the size of the enzyme and/or substrate, it has been found possible to prepare very stable enzyme-carrier composites by choosing a porous inorganic carrier material having a closely controlled average pore size related to the size of molecules which are either contained within the pores or flow through the pores.

In the case of porous inorganic carriers for enzymes, it was found that the average pore diameter should be at least as large as the largest dimension of the enzyme but no larger than about 1000 A. The upper limit of about I000 A is dictated by several observations. For example, as the average pore diameter exceeds about I000 A, there occurs a considerable reduction in surface area available for bonding of the enzymes thereby reducing the amount of enzyme which can be loaded and resulting in an inefficient composite for many applications. Further, as the average pore diameter exceeds about I000 A, any enzymes immobilized within such larger pores tend to detatch when exposed to turbulent, especially flow-through, environments. This is thought to be done to the loss of a protective effect provided by pores having an average pore diameter of more than 1000 A.

As a very practical matter, I have found that most enzymes can be successfully immobilized within the pores of porous inorganic carriers having an average pore diameter between about I A and 1000 A, preferably 100 A 500 A, the ideal pore size within that range depending on the enzyme and/or substrate size as shown in Ser. No. 332,807. Accordingly, there presently exists a need for methods of making porous inorganic carriers 2 having closely controlled average pore diameters within that range in a simple, inexpensive way.

Because of the importance of having readily controllable average pore sizes in organic suppons which are used to immobilize enzymes, recent attention has been directed to the use of porous glass particles. Porous glass is glass having minute inter-connected pores" throughout the glass particle. Such glass is made by subjecting a phase-separable glass (e.g., certain borosilicate glasses) to phase-separating heat treatments which result in an acid-soluble phase. That phase can be readily leached out with an acid leaving behind a porous network of connected channels of substantially uniform average diameter. Such porous glass can be made, for example, in accordance with the disclosures in U.S. Pat. No. 2,106,764 issued to Hood et al., U.S. Pat. No. 3,485,687 issued to Chapman, and U.S. Pat. No. 3,544,524 issued to Haller. The use of such porous glass to immobilize enzymes is described in U.S. Pat. No. 3,566,945 issued to Messing and U.S. Pat. No. 3,519,538, issued to Messing et al.

Although porous glass has been found to be an excellent carrier for enzymes because of its readily controllable pore size distribution, such carriers are relatively expensive to prepare because of the numerous and critical processing steps involved. Further, porous glass has been found to have less than desirable durability in alkaline environments where many enzymes have their pI-I optima. Because of such disadvantages associated with using porous glass, recent attempts have been made to find porous inorganic carriers which could be made relatively inexpensively and with closely controlled pore size distribution within the range of pore diameters of about 100 A to 1000 A.

In my copending application Ser. No. 344,964, there are disclosed methods for making such porous bodies which involve, very broadly, the steps of preparing a slurry of metal oxide particles of SiO M 0 TiO,, or ZrO having a particle size of 100 A to 1000 A and a binder solution containing various binders selected from acetic acid, magnesium acetate, zinc acetate, and propionic acid, drying the slurry, and then firing the resulting mixture at a temperature below that at which the material sinters. The products so formed were found to have a skeletal density approaching the theoretical density of the starting materials and a uniform porosity such that the diameters of percent of the pores was within :10 percent of the average pore diameter. I have now found that there exists another class of binder materials which can be used to prepare porous inorganic bodies, especially useful for the immobilization of enzymes. Those binder materials and methods for using them are described in detail hereunder.

SUMMARY OF INVENTION Very broadly, my method for producing 'porous bodies from SiO AI O 0,, and mixtures thereof wherein at least about 90 percent of the diameters of the pores fall within :20 percent of the average pore diameter value comprises the steps of forming a uniform slurry consisting of particles of SiO,, A1 0 TiO, and/or mixtures thereof, the particle size being substantially uniform and between I00 A and 1000 A, and an aqueous solution of a water-soluble zirconium compound; gently drying the slurry; and firing the dried material at about 450C. to about 800C. In a preferred embodiment, the water-soluble zirconium compounds are selected from the group consisting of zirconium tet- 3 rachloride, zirconium tetrabromide, zirconyl sulfate, zirconyl nitrate, zirconyl chloride, and zirconyl carbonate, and those compounds are present in concentration ranges of between about 0.0l and 2 M. The slurry made is gently dried and then fired at between about 500C.-600C. for l-3 hours.

SPECIFIC EMBODIMENTS The metal oxide particles which serve as starting materials in the preparation of the porous bodies having a substantially uniform pore size distribution in the average pore size range of 100 A to 1000 A must have closely controlled average particle sizes between 100 A and 1000 A and a surface area of at least about m /g. The general technique for the preparation of the porous bodies of this invention involves three steps. The first comprises combining the metal oxide particles with a binder solution containing water-soluble zirconium compounds at room temperature or at a slightly elevated temperature (e.g., up to about 60C., but below that at which volatilization will occur and definitely below the boiling point of the aqueous solution used). Lower temperatures to just above the freezing point can also be used, but they are generally less convenient than simply performing the mixture at room temperature. Preferably, the water-soluble zirconium compounds used in the binder solution are selected from the group consisting of ZrCl ZrBr ZrOSO ZrO(NO ZrOCl and ZrOCO at concentrations of 0.01 M to 2 M, very preferably at about 0.1 M.

After the slurry has been thoroughly mixed and made as uniform as possible, it is gently dried, preferably at an elevated temperature approaching the boiling point of the solution (e.g., 90C. to 100C), although lower temperatures can be used for longer periods. The drying step must be gentle (e.g., not at a temperature above the boiling point of the binder solution) so that the drying slurry will not be violently agitated as water is expelled. The gentle drying may be accomplished 4 characteristics to the normally negatively surfacedcharged SiO, particles such that the resulting product is ideally suitable for the adsorption of enzymes which have both positively and negatively charged groups 5 available for adsorption.

For the firing step, a temperature of at least 450C. has been found necessary with a temperature range of 500C. to 600C. being especially preferred. Temperatures up to 800C. can be used but such high temperatures require extreme caution to avoid destruction of the pores due to sintering of the material. In general, firing the green bodies for about 1 to 3 hours at 500C. to 600C. has yielded porous bodies of very closely controlled average pore diameter.

In the examples below, a variety of porous bodies were prepared from metal oxides of SiO A1 0,, TiO and a combination of SiO: and A1 0,. The starting materials consisted of particles of the above metal oxides having substantially uniform average particle sizes within the range of 100 A to 1000 A. Some of the physical properties of the starting materials used in the examples are shown in Table I.

Indicated quantities of the above starting materials were mixed with the indicated amounts of water-soluble zirconium compounds shown in Table II to form slurries of uniform consistancy which were then gently dried in air at 90C-l00C. overnight and thereafter fired at 525C. to 550C. for about l-2 hours. After cooling, the fired bodies were submitted for porosimetry analysis using conventional mercury intrusion techniques.

Table II Binder Example Solution SiO, Algog TiO Yield 1 01M ZrCl (l7ml) l0g 9.8lg 2 0.1M ZrCl, l7ml) 10g l0.2g 3 0.1 M ZrO(NO l7ml] 7.5g 3.5g 1 1.5g 4 0.1M ZrO(NO,)=, (17ml) l0g 10.07g 5 0.lM ZrOSO, (17ml) 7.5g 3.5g 1 122g 6 O.lMZrOSO (l7ml) 10g l0.lg 7 0.1M ZrBr. (17ml) 10g l0.25g 8 CLlM ZrBr, (17ml) [0g 9.72 9 0.04M ZrOCl, (325ml) lOOg l0l .Og l0 1.0M ZrOCl, (150ml) 54g 73.5g 1 l 0.04M ZrOCl, (lOOml) g 49.5g

agents has been found especially useful in maintaining a very uniform pore size distribution such that about 90 percent of the pores have a diameter within :20 percent of the average pore diameter. Further it is thought that the use of zirconium compounds enhances the overall durability of the formed porous bodies, especially the silica bodies due to the formation of zirconium silicates in the product. Further, the use of zirconium compounds is thought to add surface amphoteric For comparative purposes, the physical properties of 55 porous bodies made in accordance with the examples and controls of Ser. No. 344,964 were compared with the properties of porous bodies made in accordance with this invention. The indicated amounts of comparative materials shown in Table III were mixed and formed into porous bodies exactly as the materials of Table II were formed.

Table III (comparative porous bodies) Control Binder Sample Solution SiO Alp, TiO

A 0.lM Naqmo, "1m" 10g B H O (150ml) g 35g Table ill-continued (comparative porous bodies) 6 body was within 0 percent of the average pore diameter.

Further, the average pore diameter very closely approximates the particle size, or average particle size of Control Binder Sample 50mm" 2 3 z the starting materials, thereby permitting close control C 0.1M CH,.CO0H (17ml) lOg over the ultimate average pore size. D 0.1M I-C 8 Thus, there is provided a relatively simple and inexpensive method for making durable porous bodies having closely controlled pore distribution and average e p y p 'ep e of h Porous bethes to pore diameters within the range of 100 A to 1000 A. By fhade m t' e this thvehttoh t compared being able to tailor make closely controlled porous m Table IV wlth slmhalipl'opemesfouhd the Porous bodies within that average pore size range, there is now bottles e h aeeol'dlhg to the dlsetosure of provided another method for tailor-making porous in- 3 it significant to hcfte that the p p of organic enzyme carriers having pore sizes which maxithe porous bodies prepared using the water-soluble zirmile enzyme loading, h lfJif and Stability conium compounds compare favorably with those claim; Properties f the P -e bodies of l. A method for producing porous bodies from $0,, f h p f y data, It was fohhd that the P Size A1 0 TiO or mixtures thereof having pore diameters distribution was such that the diameters of about 90 ranging between about 100 and 1000 wherein Percent of the Pores were within about flo Percent of about 90 percent of the diameters fall within $20 perthe average P dlametercent of the average pore diameter value, which com- Table IV (Comparative Data) Metal Pore Wall Pore Diameter (A) Skeletal Sample No. Oxide Binder Vol. cc/g Porosity Max. Avg. Min. Density (g/cc) 1 SiO, ZrCl. .70 57.8 550 450 250 1.892 A sio Nac H o .81 65.3 680 510 350 2.100 2 sio ZrBr .70 58.1 580 390 250 l .83 l 3 SiO,-Al,0,, zroso .79 66.5 550 425 150 2.261 B SiO,-AI,O,, up .70 64.6 600 340 l 2. l 4 l 4 si0,-A1,0, ZrO( N0 .66 56.0 375 320 200 l .802 5 mp, zrar .48 55.2 200 I 2.288 C Alp C,H,CO0H .58 67.8 200 175 2.436 6 20,0 zrcl, .41 60.3 200 120 2.600 7 Tio zroso, .40 53.! 325 300 200 2.699 D Tio, C H ,COOH .38 63.4 288 275 220 3.960 8 Tio, ZrO(NO .34 43.3 270 260 2.563 9 510, 2:00, 0.8 61 .6 600 450 300 1.979 l0 sio, zrocl, 0.44 47.9 850 600 350 1.882 l Al,0, ZrOCO; 0.6 68.! 200A 140 3.243

40 prises:

a. forming a uniform slurry consisting of particulate From Table IV it is also significant to note that the SiO A1 0 TiO or mixtures thereof wherein the skeletal density of the porous bodies produced in acparticle diameters thereof range between 100A cordance with the present methods was relatively close and 1000A, the particle size being substantially to the theoretical density of the metal oxide starting 45 uniform, and an aqueous 0.0] to 2M solution of a materials (i about 15 percent) with the notable excepwater-soluble zirconium compound; tions of Examples 7 and 8 where TiO particles were b. drying the slurry at a temperature less than the used as starting materials. There, the shifts in skeletal boiling point of the solution; and densities were about 46 percent and 53 percent respecc. firing the dried material at 450C. to 800C. tively and the reasons for such shifts are not known at 50 2. The method of claim 1 wherein the water-soluble the present time since those samples were prepared in zirconium compound is selected from ZrCl ZrBr manners similar to Examples l-6 and 9-l l. ZrOSO ZrO(NO ZrOCl and ZrOCO The most significant feature of Examples 1-1 1 how- 3. The method of claim 2 wherein the firing of step ever is that the porosimetry data indicated such a (c) is at a temperature of 500C. -600C. for about 13 closely controlled pore size distribution that the diame- 55 hours. 7 ters of about 90 percent of the pores of each porous 

1. A METHOD FOR PRODUCING POROUS BODIES FROM SIO2, AL2O3, TIO2 OR MIXTURES THEREOF HAVING PORE DIAMETERS RANGING BETWEEN ABOUT 100A AND 1000A WHEREIN ABOUT 90 PERCENT OF THE DIAMETERS FALL WITHIN 20 PERCENT OF THE AVERAGE PORE DIAMETER VALUE, WHICH COMPRISES: A. FORMING A UNIFORM SLURRY CONSISTING OF PARTICULATE SIO2, AL2O3, TIO2, OR MIXTURES THEREOF WHEREIN THE PARTICLE DIAMETERS THEREOF RANGE BETWEEN 100A AND 1000A, THE PARTICLE SIZE BEING SUBSTANTIALLY UNIFORM, AND AN AQUEOUS 0.01 TO 2M SOLUTION OF A WATER-SOLUBLE ZIRCONIUM COMPOUND, B. DRYING THE SLURRY AT A TEMPERATURE LESS THAN THE BOILING POINT OF THE SOLUTION, AND C. FIRING THE DRIED MATERIAL AT 450*C. TO 800*C.
 2. The method of claim 1 wherein the water-soluble zirconium compound is selected from ZrCl4, ZrBr4, ZrOSO4, ZrO(NO3)3, ZrOCl2, and ZrOCO2.
 3. The method of claim 2 wherein the firing of step (c) is at a temperature of 500*C. - 600*C. for about 1-3 hours. 